Adding support checks for WebSocket.

sdk/lib/html/dart2js/html_dart2js.dart

 library html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
 import 'dart:math';
 import 'dart:svg' as svg;
@@ skipping 21053 matching lines @@
   /// @domName WebKitNamedFlow.removeEventListener; @docsEditable true
   @JSName('removeEventListener')
   void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]) native;
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 /// @domName WebSocket; @docsEditable true
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@SupportedBrowser(SupportedBrowser.IE, '10')
+@SupportedBrowser(SupportedBrowser.SAFARI)
 class WebSocket extends EventTarget native "*WebSocket" {
 
   ///@docsEditable true
   factory WebSocket(String url) => WebSocket._create(url);
   static WebSocket _create(String url) => JS('WebSocket', 'new WebSocket(#)', url);
 
+  /**
+   * Checks if this type is supported on the current platform
+   */
+  static bool get supported => JS('bool', 'typeof window.WebSocket != "undefined"');
+
   /// @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent; @docsEditable true
   WebSocketEvents get on =>
     new WebSocketEvents(this);
 
   static const int CLOSED = 3;
 
   static const int CLOSING = 2;
 
   static const int CONNECTING = 0;
 
@@ skipping 5838 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }